Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

This commit was generated by cvs2svn to compensate for changes in r121642,
which included commits to RCS files with non-trunk default branches.

Import beta6 of libuwx. This release has some minor fixes and
some minor corrections to beta5.

This is beta4 of libuwx; an ia64 stack unwinder. This code is made
available by Hewlett-Packard under the MIT license. The unwinder is
small, clean and fast and needed little adaptation for use in the
kernel.

This import has embedded in it the changes needed to make it build
in a kernel environment.

To optimize the common case, the kernel will minimize the number
of registers saved by not saving the preserved registers. In case
access to preserved registers is needed (signal handling, ptrace)
the kernel will unwind to the context of the syscall or exception.
For this we need an unwinder.

Approved by: re (blanket)